Use the same structure for vehicle hardpoints and item ports

[alistair3149]

Issue:
The hardpoints from the Vehicle API is very similar to the ports from the Item API, yet they are using different keys which makes it confusing.

Suggestion:
The Vehicle API should use the same syntax as Item API so that it is more intuitive and maintainable. Since it is a massive change, I suggest bumping up the vehicle API to v3 while keeping v2 for backward compatibility.

Current key in Vehicle API	Suggested change to match Item API
hardpoints	ports
min_size	sizes.min
max_size	sizes.max
type	compatible_types.type
sub_type	compatible_types.sub_type
item	equipped_item
item.children	equipped_item.ports